Remote control system



June 19, 1945. B. DEAL 2,378,540

- REMOTE CONTROL SYSTEM- Original Filed July 25, 1941 ,II "3 INVENTOR jHgrnwnB.fia/L ATTORNEY Patented June 19, 1945 UNITED sTATE;

f PTENT' OFFICE REMOTE CONTROL SYSTEM Harmon B. Deal, Glen Ridge, N. J., assignor to Radio Corporation of America, a corporation of Delaware Original application July 23, 1941, Serial No.

403,736, now Patent No, 2,340,798, dated February 1, 1944. Divided and this application October 16, 1942, Serial No. 462,252

' 4 Claims j nation, or to .a certain class of people such as air wardens, an impending condition or action and to-issue necessary instructions to them. To this end it is an object-of the present invention to permit a broadcasting station toturn on all receivers, or a certain group of receivers, within range which are equipped with an attachment made'in accordance with the present invention, and also, to turn the receivers off. The scheme contemplated herein is feasible from all View pointsfor-either the sound broadcast band or the ultra-high frequency band. While the various features of the invention are of the greatest importance in'connection with the turning on and off of radio receivers from a transmitting point, it will be appreciated by those skilled in the art that by simple extensions of the method and arrangements herein disclosed,'the number of'control functions maybe increased to any desired extent. .I-Ioweverythe' on and off functions. are,ina sense, primary and should properly precede inclusion of any additional controls which may prove desirable. :Accordingly, the invention will be de scribed; in connection with a simple on and oil control. In accordancewith the present invention, control;si'gnals which :are preferably, though not necessarily, generated at" the broadcast station are utilized to modulate the'carrier of the broad cast station which is to exercise control.- Of course, if desired' 'an auxiliary special carrier may'be'modulated.

If, a remote receiveris to be controlled only as toon andoif, and-the stations regular carrier isto bemodulated by the control signals, it .-is immaterial whether or notthe controlling signals are audible since the control signals. would normally precede the start, and follow the termination of the special broadcast that was the occasion'for turning thereceiver on. However, itis evident that under certain circumstances, an inaudible :eontrol signal'is tobe preferred, 'as'for example in the case wherethere may have been :in progress a program to which many people were already listening and to whom an audible control signal would be objectionable, or

in cases .where a certain amount of secrecyis desirable.

Inaudibility of the control signal maybeobtained by. utilizing super-audible orsub-audible control frequencies. Since super-audible frequencies would encroach on adjacentbroadcast' channels, sub-audible control frequencies are preferred. Another reason for preferring the sub-audible frequency band for the controlfrequencies is because it is immediately, available since it is'not being used presently. The average radio receiver and loudspeaker cut off below cycles per second, and even the very best receivers with considerable bass compensation do not transmit frequencies below 50 cycles per second'to any, appreciable extent. 'This indicates that a band in which control signals will not affect program material being broadcast simultaneously, lies below 50 cycles per second. Itis recognized, of course, that the low frequency outoff of a receiver is not abrupt, and that therefore the lowest usable frequency and amplitude of the'control signalswill produce the leastprogram interference. I f

In a series of tests which have been conducted with devices built in accordance with'the present invention, it has been found'that the amplitude of the controlsignals should be kept as small as possible for the'reason that harmonics of the control frequency, whether originating in the source or produced in the receiver, will lie the acceptance band of the usual radio receiver and will be audible. The harmonics may be produced in the receiver by overload or by cross-modulation of control frequencies and program, and it j Briefly, the invention provides means at the transmitter for producing the control frequencies which may comprise an oscillation generator tube and modulating means for modulating the carrier of the transmitter with the control signals. At the receiver, means are provided for receiving the modulated-carrier and utilizing the derived signals for control purposes. This last-named means may comprise a small radio receiverkwhich may be made very simple and inexpensive if its function is to operate only on control signals. q

Referring now to the drawing, which shows a suitable controlsignal generating means which may be used at a transmitting station, there is provided an electronic tube I which is employed as an oscillator to generate the various desired control frequencies. For this purpose a novel phase reversal circuit arrangement is used for providing phase reversal between the grid and plate of the oscillator tube I. The phase reversal network is connected between the anode and cathode of the tube and comprises capacities I, 8, and 9 and resistors I and II. This, network, also, determines the frequency of the generated oscillations in accordance with the values of the resistances and the condensers. Resistors Ill and II are normally shunted by resistors I4 and I3 respectively, one shunt circuit extending from a junction point 26: through a switch contact I8, through resistor I4 and thence to a junction between resistors I0 and II.' The other shunt circuit extends from a junction point 25 through switch contact l1, through resistor I3 and thence to the junction between resistors I0 and, II. Feedback between the plateand the grid is provided by'a circuit 24 which connects point 26 of the phase reversing circuit to the input grid of tube I through a coupling condenser 3. In order to avoid undesirable phase shifts in the resistance of the grid coupling circuit, a high resistance grid leak resistor 2 is provided.

Preferably the resistance of resistor 2 should be large as compared to the reactance of condenser 3. Two control push buttons I6 and are provided. Push button 20 acts upon depression to close a switch 2|, and thereby connects the output of the oscillator I to the amplifier 23. Push button I6, on the other hand, acts when depressed to open switches l1 and I8 and close switch I9. Normally resistor I3 is connected in parallel with resistor II, and,'likewise, resistor I4 is connected in parallel with resistor I0. Under these conditions the net resistance between points and 26 of the network is decreased. This results in: a higher frequency of oscillation. Consequently, with push button I6 not depressed, and push'button 20 depressed, control oscillations of a certain frequency are'impressed, upon the amplifier 23 through closed switch 2! and conductor 22.

When push button It is depressed, the parallel resistors I3 and I 4 are disconnected from the phase shifting circuit thereby resulting in a higher net resistance between points 25 and 26 and therefore providing a lower output frequency, it being noted, that the new frequency is fed to the same outputamplifier 23 through conductor 22 due to closure of switch I9. In the condition shown, the oscillator I is operating at a frequency which is-determined by resistors II), II, I3, and

I 4, and the oscillations of this frequency will be impressed upon the amplifier 23 upon closure of switch 2|. Hence, depression of push button 20 will impress this control frequency upon the transmitter where it is utilized to modulate the carrier of the. transmitter in accordance With well known practice.

It should be noted that. resistors I0, I I, I3; and I4 are preferably variable resistors so as to permit adjustments. Also, unicontrol means I2 is provided to adjust resistors I0 and I I simultaneously, and unicontrol means I5 is provided to permit simultaneous adjustments of resistors I3 and I4. Ifit is desired to transmit the other control frequency, it is only necessary to depress push button I6 as previously described.

While I have indicated and described a system for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organization shown and described, but that many modifications may be made without departing from the scope of my invention, as set forth in the appended claims.

What I claim is:

1. In an oscillator system of the type provided with a tube having. at least a cathode, a control grid and a plate, a phase reversal network connected between the plate and cathode, said network consisting solely of resistive and capacitive elements, means for varying the number of resistive elements to be included in said network, thereby to shift the networks frequency characteristic from one to the other of two predetermined values, a feed back circuit connected between the output terminals of the reversal network and the grid, and a pair of push button switches, one of said switches constituting means for applying oscillatory energy of one frequency to a utilization deviceand for switching out of said network certain of its resistive elements, and the other of said switches constituting means for applying oscillatory energy of the other frequency to said utilization device while the full complement of resistive elements is retained in said network.

2. In an oscillator circuit for producing subaudible modulation frequencies for a high frequency carrier, a tube having at least a cathode, an anode, and a control electrode, a frequencydetermining circuit connected between the anode and cathode, said circuit consisting of at least a pair of series-arranged resistors, a respective condenser connected from each resistor terminal to the cathode, a feedback connection from the output terminal of said resistors to said control electrade, and manually controllable means including two push button switches so organized that one of them increases the resistance valueof said resistors and also feeds a predetermined one of said modulation frequencies to a utilization device, whereas the other of said switches oper-' ates solely to feed another of said modulation frequencies to said utilization device.

3.-In an oscillator circuit for producing subaudible modulation frequencies for a high frequency carrier, a tube having at least a cathode, an anode, and a control electrode, a frequencydetermining circuit connected between the anode and cathode, said circuit comprising a pair of seriesarranged resistors and three condensers, each condenser being connected from the cathode to a different one of the resistor terminals, a feedback connection from the output terminal of said resistors to said control electrode, a second pair of series-arranged resistors, means including normally closed switch contacts for connecting in parallel the two pairs of resistors, thereby to produce a certain frequency response in said frequency determining circuit, push button means for opening said contacts, thus producing a different frequency response, said push button means being also effective to close an output circuit from said frequency determining circuit to a utilization device, and additional push button means for closing saidxoutput circuit while the closure of said switch contacts is maintained.

4. In an oscillator circuit for producing subaudible modulation frequencies for a high frequency carrier, a tube having at least a cathode,

cathode, said circuit consisting of two parallelconnected pairs of series-arranged resistors, condensers connected from each terminal of the resistor pairs and from an intermediate junction thereof to the cathode, a feedback connection from output terminal of said resistors to said control electrode, said resistors and condensers bein chosen in magnitude to cause said oscillator to produce oscillations of one or another of two predetermined sub-audible frequenciesa resistance of high magnitude connectedbetween the control electrode and cathode to avoid undesirable phase shifts, and means including push button control switch contacts arranged in two groups such that a first group controlled by one push button comprises normally closed pairs of contacts which constitute interconnections between the terminals of said resistor pairs, and when opened said contacts isolate one said resistor pair from the frequency-determining circuit, said switch contacts of that group also including means for feeding oscillatory energy to a utilization device, the other of said contact groups being arranged for operation by a second push button and constituting means operable solely to feed oscillatory energy to said utilization device "during the parallel-connection of said resistor pairs, whereby one or another of two predetermined sub-audible frequencies is delivered to said utilization device.

HARMON B. DEAL 

